Pygopagus

Pygopagus twins are conjoined twins that are joined in the dorsal aspect, facing away from each other.

They share the sacrococcygeal and perineal regions. Fusion of sacrum and coccyx frequently occurs. The dura and the spinal cords may be fused in as many as 1/3rd of the cases.The anus, rectum, bladder and urethra may be seen fused. External genitalia fusion is very rare. Limbs, upper body and intestines are usually separate.

MRI is important to assess the spinal cord fusion and to assess the feasibility of separation. Angiography may be needed to assess the pelvic vessels which may anastomose freely.